This type of antenna comprises a conducting element arranged on the dielectric substrate and defining a slot having parallel edges. Such an antenna is already described in the document EP 0 766 152 in the name of the present applicant. FIG. 1 shows the antenna described in this document. This slot antenna 11 consists of a printed circuit conducting element 12 attached to a dielectric substrate 13. This substrate is preferably of a flexible material to allow the arrangement of this antenna in an assembly groove of a horologic case in such a way that the antenna may be rolled around this case. A radiating slot 14 is formed in the conducting element. This antenna is connected to an antenna circuit comprising a micro receiver-emitter 15 which is located in the horologic case. The connection between the antenna 11 and the micro receiver-emitter 15 is carried out at two excitation points 16 and 17, normally by a transmission line such as a coaxial cable. This coaxial cable may be considered as the output of the antenna circuit. As the output of the antenna circuit is asymmetrical, it is necessary to adapt the symmetric antenna to this output. Thus, a conversion device is necessary which is mounted between the symmetrical antenna and the asymmetrical output. Such a device is known to the skilled person by the term "balun" (for balanced-to-unbalanced). This "balun" is generally obtained by using discrete elements, such as a condensator and/or a certain length of the line. In the above-mentioned document, the transmission line 18 connected an excitation point 16 via an adaptation condensator C (see FIG. 1) to micro receiver-emitter 15 of the antenna circuit, and the other excitation point 17 is connected to the mass. The value of the condensator naturally depends on the used frequency, but may be around several pico-farads for the applications described in this document. It may thus be understood that such a "balun" is not very practical, is large in size and is expensive.
However, for aesthetic reasons, and because of the size and price etc., (criteria which are particularly important in horological technology), solutions are searched for allowing to reduce cost and to simplify the assembly, the excitation, as well as the adaptation of such an antenna.